The present invention relates to a continuous process for manufacturing soap thickened grease compositions containing water soluble additives, e.g. additives useful for imparting to such grease compositions improved properties such as corrosion resistance and/or extreme pressure wear properties.
Continuous processes for manufacturing soap thickened grease compositions are known in the prior art. For example, U.S. Pat. No. 3,475,335, issued Oct. 28, 1969 to John H. Greene, et al, discloses a process wherein a saponifiable material, (fatty acids, etc.) is mixed with an inorganic base (lithium hydroxide, etc.), in a tubular reactor, in the presence of water, at saponification conditions of temperature and pressure for forming a soap, wherein the reaction mixture from said tubular reactor is dehydrated, in a dehydrator vessel, at reduced pressure; wherein soap containing material from said dehydrator, is recirculated through a shear valve for improving the rate of dehydration and for conditioning the soap; and wherein a continuous stream of dehydrated soap containing material withdrawn from said dehydrator is intimately mixed with oil to form a grease product. Additives, particularly water soluble compounds useful as corrosion inhibitors and/or as additives for improving extreme pressure wear properties, are preferably added, as non-aqueous mixtures, to the dehydrated soap-containing material immediately prior to mixing oil therewith.
U.S. Pat. No. 3,488,721, issued Jan. 6, 1970 to Richard L. Frye, discloses a method of preparing a water-free oil-additive slurry for addition to a soap thickened grease.
In such methods of the prior art, as described above, the preparation of an oil-additive slurry which is sufficiently dispersible in a grease product is difficult, and requires additional process steps. Considering the process of U.S. Pat. No. 3,488,721, a water solution of an oil-insoluble additive is mixed with an amount of oil to form an emulsion. This emulsion is heated under conditions of high shear mixing for driving water therefrom and to yield a slurry of said additive in oil, wherein the additive particle size is sufficiently small (less than 10 microns) for incorporation into a grease product. Difficulties are encountered in preventing agglomeration of additive materials present in the oil slurry into particles sufficiently large to impart a grainy appearance to the grease product.